The overall goal of this Technical Core is to provide support to the other projects in the Program, where there is special expertise/capability or where establishing a core facility is particularly efficient and cost effective. The support will be in: *quantification of photosensitizer concentration in tissues ex vivo, *confocal fluorescence microscopy of tissues and optical phantoms, *optical instrumentation for light delivery and light/photosensitizer dosimetry, *optical calibrations and provisions of well-characterized optical phantoms, *maintenance of an Internet hub for image/data storage and communication between laboratories. Procedures such as photosensitizer quantification and confocal fluorescence microscopy are appropriately handled within a core facility because of the ability to establish proper quality control and, hence, to provide accurate and reliable results in a timely manner. All projects will utilize these services. Optical instrumentation plays a key role in most of the projects, particularly the clinical studies, and the Core will enable instruments to be tailored to the specific needs of each project, rather than relying on either the limited available (and expensive) commercial equipment or having each laboratory construct its own with limited expertise and equipment to do so. Similarly, the calibration procedures and optical phantoms which will be provided through the core will ensure consistency between the projects. The provisions of an Internet hub will maximize communication between the projects and ensure that data generated within the Core will be disseminated rapidly and efficiently. While the primary purpose of the Technical Core is to provide essential support to the other projects, the developmental work required will be productive in its won right, especially in the areas of optical instrumentation and fluorescence analysis of tissues.